This invention relates generally to electrical relays, and more particularly, to a pre-charge component for an electrical load.
Relays are electrical switches that open and close based on an applied electrical current. Different relays may be used for different types of applications or based on certain operating parameters. The relays are typically of an electromagnetic or solid state type. In high voltage applications, the relays must be designed to handle the effects of the high voltage. For example, in hybrid electric vehicles (HEVs), very large integrated capacitors, such as, larger than 2000 micro-Farads (μF), may be provided to power one or more loads. The capacitor(s) in this type of application must be pre-charged to avoid a damaging inrush current being applied to the relay contacts when power is switched on. Essentially, when power is applied to an uncharged capacitor an excessive amount of current rushes to the capacitor. The large inrush of current may cause excessive heating and decrease the life of the capacitor if a pre-charge circuit is not provided. The large inrush of current also can damage the relay contacts that switch power to the capacitor. Further, the main disconnect relay would need to be very large if the pre-charge circuit were not present and the system fuse also may be tripped more easily and more often without the pre-charge circuit.
Currently, in these high voltage applications, the pre-charge module is typically an electromechanical relay capable of switching a large voltage, such as 300V to 600V. The pre-charge module is used in series with a resistor across the main contacts of a contactor to pre-charge the capacitor(s). However, these high voltage electromechanical pre-charge modules are very expensive and usually larger in size. Thus, the overall cost of the system is increased and the size of the module including this relay also may be larger, thereby limiting the space for other components.